As is now well-known in the art, the term polymer refers to a molecule made up by the repetition of simpler units often referred to as the mer or monomer units. Synthetic polymers can generally take one of two structural forms; in one form, they are linear polymers in which case the monomeric units making up the polymer are linearly arranged. Alternatively, the polymer structure may be branched in which portions of either the backbone or individual repeating units are discrete and emanate from the backbone of the polymer.
Thus, the simplest linear polymers may be represented by polyethylene and polypropylene in which repeating ethylenic units form the linear chain. In polypropylene, the polymer is made up of repeating ethylene units, each having pendant methyl groups extending therefrom. It is, of course, well-known that both polyethylene and polypropylene can be formed as branched polymers, by reactions such as free radical reactions. In such crosslinked polymers, many of the individual branches of the polymer extend from the linear polyethylene and polypropylene chains. It is, of course, also possible to introduce crosslinking monomers to crosslink linear chains each with the other.
Branching of the type referred to above is random in nature. For that reason, it is generally not possible to either control the extent of branching or the composition of the branches.
Various types of more complex branched polymers are known in the art. One such example includes the so-called star polymers such as those described in U.S. Pat. No. 3,985,830. In such star polymers, the molecule is formed from a nucleus from which polymeric arms extend in a radial fashion. In the star polymers of the type described in the foregoing patent, the molecular weight of the nucleus is essentially negligible as compared to the molecular weight of the polymer as a whole. The polymer system described in the foregoing patent utilizes what is known in the art as a living catalyst in which the chain growth of various branches begins essentially simultaneously and continues until terminated by the addition of a monomer to stop chain growth.
Another type of branching, sometimes referred to as a comb, is produced when branches extend, either regularly or irregularly, from a polymeric backbone.
Various attempts have been made in the prior art to provide methods for linking polymer chains. For example, in published Japanese Application No. 58-217505, there is described a technique to increase the molecular weight of polymers of ethylene, or copolymers of ethylene or other alpha-olefins, in which two polyolefin chains are bonded together or coupled by means of disiloxane. In the teachings of that patent application, there is described a high temperature technique for producing polyolefins which inherently provides polymer chains having a relatively low molecular weight. Thus, the patent teaches that the molecular weight, and hence viscosity, of the polymer chain, can be increased by coupling together two of the chains. Thus, the published Japanese application does not disclose or suggest a technique to provide highly branched polyolefins.
In published Application No. WO87/03603 there is purportedly described a technique for producing polyolefin star polymers. In one example, there is described nodular ethylene propylene copolymers in which ethylene, propylene and norbornadiene are copolymerized to form a nodular branched structure to which additional monomers are added to lengthen the nodular arms. Methylacrylate is then added to cap the arms. Another example purports to describe the reaction of a hydroxy terminated ethylene propylene copolymer which is then dissolved in a dry lubricating oil and reacted with a polyfunctional isocyanate. No reaction conditions of any kind nor any structural characterizations of the polymer are provided.
Thus, there is a need to provide highly branched polymer structures and techniques for their production which overcome the foregoing deficiencies of the prior art.
It is an object of the present invention to provide highly branched polymers in which the branches are formed from polyolefin polymers.
It is a more specific object of the invention to provide highly branched polymers in which polyolefin arms are linked to a polymeric backbone to provide a highly branched polymer structure, characterized as a comb, star, nanogel or combinations thereof.
It is yet another object of the invention to provide highly branched polymers and a technique for the preparation of highly branched polymers containing polyolefin arms in which it is possible to control the composition of the polyolefin arms as to the type of monomer(s), quantity of monomer(s), monomer distribution, molecular weight and molecular weight distribution.
It is a further object of the invention to provide highly branched polymers and a technique for their preparation in which it is possible to control the composition of the polymer by controlling the degree of branching or number of arms coupled to the polymer backbone.
It is a final object of the invention to provide comb, star, nanogel type branched polymers wherein the polyolefin arms can be post functionalized by other chemical reactions.